A known automobile is provided with a seat belt or an airbag as an equipment to secure safety of a passenger. The known automobile includes a function which adjusts a speed of the airbag for deployment and a gas amount of the airbag for deployment and adjusts a pretention of the seat belt by determining whether a passenger is an adult, an infant or a child in accordance with a weight of a passenger to enhance the performance of the seat belt and the airbag. From an aspect of the security of a passenger, it is extremely important to precisely determine a load of a passenger by detecting the weight thereof.
Generally, load sensors (load cells) are placed at four corner positions of a seat frame as an apparatus for detecting the weight of a passenger. By adding the load applied to the load sensors in a longitudinal direction together, the weight of a passenger may be generally obtained. However, the load sensor is configured with a strain gauge affixed to a strain body which bends when the load is applied, and outputs voltage signals which change in response to a changing amount of a resistance value associated with flexural deformation of the strain body in response to the load. The strain body is designed to have intensity high enough to measure the weight of a passenger sensitively and may be abnormally deformed when a large impact is applied to the strain body due to, for example, a collision of the vehicle because an excessive load is applied to the strain body. In those cases, because the detection criteria of the load sensor may include discrepancies, the load sensor cannot measure the weight of a passenger precisely.
A passenger weight measuring device is disclosed in JP4267836B (hereinafter referred to as Patent reference 1). As disclosed in Patent reference 1, the passenger weight measuring device includes a load detection means detecting a load in response to an acceleration velocity applied to a passenger and a seat in response to, for example, a weight of a passenger and a collision of a vehicle. The passenger weight measuring device further includes an abnormal load detection means outputting an abnormal load signal in a case where the abnormal load which is out of a preset load detection range is detected by the load detection means. Accordingly, even if the vehicle has a collision at a low speed with a passenger of higher weight (which is in a case where the abnormal load is applied to the strain body), the weight measuring device precisely determines whether an abnormal load is applied to the vehicle and terminates the control for deploying the airbag in accordance with the weight of a passenger.
A vehicle impact determination device is disclosed in JP2011-43454A (hereinafter referred to as Patent reference 2). The vehicle impact determination device determines that an impact is applied to a vehicle in a tensile direction in a case where a load which is equal to or higher than a predetermined value is detected within a predetermined time after a compression load which is equal to or higher than the predetermined value is detected at a position close to a seat for the vehicle. In a case where the impact is applied to the vehicle due to, for example, a collision of the vehicle, the vehicle impact determination device determines, for example, the impact in response to a phenomenon in which a compression load and a tensile load are applied alternately and consecutively within a predetermined time at a portion close to the seating portion of the seat for the vehicle. The vehicle impact determination device includes an impact alert means for notifying a passenger of the vehicle that the vehicle is impacted when determining, for example, the collision of the vehicle. The passenger weight measuring device disclosed in Patent reference 1 and the vehicle impact determination device disclosed in Patent reference 2 prevent relevant devices which activates in response to an inaccurate detection from operating wrongly in a case where the load detection device may possibly detect an inaccurate value due to the collision of the vehicle.
However, when a passenger parallel parks a vehicle in Europe, a vehicle on a passenger may repeatedly collide with vehicles parked in a front-rear direction to secure a parking space. Usually, in those circumstances, a passenger distinction performance of the load sensor is not influenced because of a minor collision of the vehicle.
However, in those circumstances, the passenger weight measuring device disclosed in Patent reference 1 and the vehicle impact determination device disclosed in Patent reference 2 may indicate an alert (impact influence alert) by detecting the minor collision of the vehicle and may increase a frequency to have a vehicle check-up at a dealer or at a maintenance shop of the vehicle to deal with the alert.
A need thus exists for a seat apparatus for a vehicle which is not susceptible to the drawback mentioned above.